This invention relates generally to systems for connecting implements to tractors and deals more particularly with a system which allows mounted implements utilizing rear wheel lift assist units to interface with a three point hitch of a tractor in a way which prevents damage to the three point hitch.
A variety of systems for connecting implements to a tractor have been developed in which the implement is connected to the tractor by way of a conventional three point hitch. In a three point hitch, the two lower links or arms are driven by the hydraulic system of the tractor to provide operator controlled lifting and lowering movement of the lower links and, likewise, to the associated implement connected to the lower links. The single, upper or stabilizing link of a three point hitch typically is used to maintain a particular horizontal pitch orientation of an implement or to transmit a positive down pressure force to tillage tools mounted on the frame portions of the attached implement.
During the use or transportation of an implement, a number of forces can be developed on the three point hitch, the implement and the implement lift support structure. The three point hitch can provide upward lift by actuating the power lift features of the two lower support arms of the hitch. For example, the upward force is utilized for lifting and carrying an implement during transport from one location to another. During usage of a tillage implement, the two lower lift arms of the hitch and the upper top link operate in concert to orient the implement to ensure proper ground penetration of the tillage tools.
Because of the size and weight of many implements, they cannot, in practice, be totally disengaged from the ground simply by utilizing the upward force of the two bottom links of the three point hitch and an attempt to lift such an implement will result in damaging the tractor hydraulic lift circuit and/or impeding tractor stability. Thus, when using particularly heavy implements, it would be impractical or even impossible to carry the full weight of the implement in cantilever fashion on the three point hitch. Such an attempt, in certain combinations of tractors and implements, would simply act to raise the front wheels of the tractor off of the ground while leaving the implement fully in contact with the ground. In such systems where the three point hitch of the tractor is ineffective for disengaging the implement from the ground, a trailing lift assist support system is typically used to support the main frame of the implement. The lift assist system typically employs one or more ground engaging wheels which are designed to, during lift and transport, contact the ground and carry some of the load of the implement. A power lift means, such as a hydraulic lift cylinder, is normally included for actuation from the hydraulic system of the tractor when it is desired to transfer a portion of the weight of the implement to the ground engaging wheel of the trailing support system. Thus, the cooperation between the wheeled lift assist support system and the three point hitch system acts to provide lifting of the implement. The use of the rear wheel lift assist system is not limited to merely transporting the implement, but is also used when an implement is to be lifted clear of the ground such as for turning at the end of a field and the like.
It is to be appreciated, however, that when the weight of the implement is supported, in part, by the rear wheel trailing support system, the entire system of the tractor and the trailing lift support members acts as a rigid, fixed body with the implement being carried thereby. During transport of the implement in this lifted position, the tractor may be tilted in pitch with respect to the rear lift support system, as the combination of the two pass over uneven terrain. The system must accommodate this difference in pitch between the tractor and the trailing support system in order to avoid damage to the three point hitch upper link due to excessive compression loads between the tractor and the trailing support system.
Various arrangements of linkages have been proposed for providing yieldable interconnections between three point hitches and the trailing frames of implements; however, most such systems are not adapted for tool bar type implements (i.e. where a plurality of relatively independent tool gangs are attached to a transversed tool bar and are vertically movable relatively independent of one another within the range of their operative engagement with the soil). Such tool gangs typically trail the tool bar and have integrated down pressure means on each gang unit. Such gang units typically comprise cultivators, rotary hoes, planters and the like. Application of orientation forces on the tool bar from the tractor remains desirable in many instances to control and selectively increase or decrease the effective down pressure forces across all of the individual gang units. However, there is no integrated frame rearward of the tool bar for transmitting such forces to the units. Therefore, the forces must be applied through the tool bar itself. At such time, stress relief must be provided for the hitch linkages to avoid damage due to excessive compressive loads exerted on the three point hitch by the upper link trailing support system.
Thus, it can be seen in U.S. Pat. No. 4,903,781 that a system is set forth for flexibly mounting agricultural implements. Although the system set forth in the '781 patent does appear to be effective for the above stated purpose, it is generally believed that the mechanism set forth therein to accomplish the flexing between the tractor and the rear lift support system is more complicated, and accordingly, more costly than need be.
Thus, it is an object of this invention, to provide an implement which is capable of isolating the three point hitch of a tractor from excessive compressive loads which would otherwise damage the three point hitch, the tractor or the implement.